1. Field of the Invention
The present invention generally relates to a chemical vapor deposition (CVD) chamber. More particularly, the present invention relates to an improved susceptor used in a CVD chamber.
2. Background of the Related Art
CVD vacuum chambers are useful for depositing thin films on semiconductor substrates. Generally, a precursor gas is flown into a vacuum chamber through a gas distribution system and reacts with a heated substrate surface to deposit a thin film thereon. The deposition gas reaction also forms volatile by-product gases which are pumped away through a chamber exhaust system. Typically, a susceptor or substrate support member is provided to secure the substrate during the deposition process as well as to heat the substrate to the required processing temperature. Furthermore, a purge gas is flown towards the backside and/or edge of the substrate during processing to prevent deposition on the backside and the edge of the substrate which tends to flake off and contaminate the chamber. Exemplary CVD chambers are disclosed in U.S. Pat. Nos. 5,516,367 and 5,476,548, both of which are hereby incorporated by reference.
To increase manufacturing efficiency and device capabilities, the sizes of the devices formed on a substrate have decreased while the number of devices formed on a substrate has increased. Uniform CVD deposition across the surface of the substrate has become increasingly important to form uniform devices on substrates and to maximize the number of devices that can be formed on the substrate. Moreover, reduction of particle contaminates generated in the chamber has also become increasingly important to produce functional devices.
FIG. 1a is a partial cross sectional view of a substrate 14 supported on a susceptor having a purge gas channel 30 surrounding the edge of the substrate. FIG. 1b is a partial top perspective view of the substrate 14 supported on the susceptor showing the purge gas channel 30 surrounding the edge of the substrate. As shown in FIG. 1a, the substrate 14 is releaseably secured on the susceptor surface by a vacuum chuck having vacuum channels 20 which are connected to a vacuum pump (not shown), and the edge of the substrate is surrounded by a purge gas channel 30. A purge gas feed line 22, preferably disposed within the susceptor 10, feeds a purge gas into the purge gas channel 30 surrounding the edge of the substrate 14, thereby inhibiting the process gas from coming in contact with the substrate edge and depositing thereon. Preferably, a plurality of purge gas feed lines 22 supply purge gas into the purge gas channel 30 to achieve even distribution of the purge gas to the edge of the substrate.
Generally, the purge gas flows past the edge of the substrate 14 and outwardly away from the center of the substrate. However, because a substrate typically includes a notch 16 at the substrate edge as an identifying mark of the type and the orientation of the substrate, an excess amount of purge gas passes through the notch, diluting the processing gases adjacent to the notch and preventing formation of functional devices in the region adjacent to the notch. FIG. 1b shows the effects of the purge gas, as indicated by the arrows, in the region adjacent to the notch. Typically, deposition in the region adjacent to the notch 16 is non-uniform because the excess purge gas coming through the notch creates an area of exclusion on the substrate. Thus, the region adjacent the notch 16 is wasted because of improper processing.
A similar purging effect in the region adjacent the notch occurs in a processing system where a purge guide is used for controlling the purge gas. FIG. 2a is a partial cross sectional view of a purge guide 26 in combination with a substrate 14 disposed on a susceptor 10 in a processing position. FIG. 2b is a partial top view of a purge guide and a substrate having a notch 16, showing the effects of the purge gas in the region adjacent the notch. As shown in FIG. 2a, the substrate 14 is supported by the susceptor 10 and releaseably secured on the susceptor surface by a vacuum chuck having vacuum channels 20 which are connected to a vacuum pump (not shown). When the susceptor 10 is moved to a processing position, the purge guide 26 rests on the susceptor 10, preferably on a plurality of anti-sticking grooves 21, and a shield portion 12 of the purge guide 26 extends over the edge of the substrate 14. The shield portion 12 of the purge guide 26 maintains a fixed gap, typically between about 2 and about 10 mils, above the substrate 14 through which the purge gas flows as the gas continues into the processing area of the CVD chamber. It is important to maintain a consistent gap around the edge of the substrate 14 to control the purge gas distribution so that a uniform center to edge deposition on the substrate can be achieved.
A purge gas feed line 22, preferably disposed within the susceptor 10, feeds a purge gas into a purge gas opening 24 between the purge guide 26 and the susceptor 10. The purge guide 26 then guides the flow of purge gas, as shown by the arrows, to the edge of the substrate 14, thereby inhibiting the process gas from coming in contact with the substrate edge and depositing thereon. Preferably, the purge gas opening 24 completely surrounds the edge of the substrate, and a plurality of purge gas feed lines 22 supply purge gas into the purge gas opening 24 to achieve even distribution of the purge gas to the edge of the substrate.
However, an excess amount of purge gas passes through a notch 16 on the substrate, diluting the processing gas adjacent the notch and preventing formation of functional devices in the region adjacent the notch. FIG. 2b shows the effects of the purge gas, as indicated by the arrows, in the region adjacent the notch. Typically, deposition in the region adjacent the notch 16 is non-uniform because the excess purge gas coming through the notch 16 creates an area of exclusion on the substrate. Thus, the region adjacent the notch 16 is wasted because of improper processing.
Therefore, there remains a need for an apparatus for supporting a substrate in a processing chamber which delivers a purge gas to the edge of the substrate and prevents excess purge gas from causing non-uniform and inconsistent deposition at the region adjacent the substrate notch.